Candidate Gen. Sarath Fonseka accused Rajapaksa of intimidation during the country's first peacetime presidential election in more than two decades and said his staff had received threatening phone calls

Army soldiers and commandos tried to enter the Cinnamon Lakeside Hotel shortly after Fonseka and opposition party members arrived Tuesday, the former general told CNN. His security forces told the soldiers they could not enter the building, so they stayed outside, Fonseka said.

Fonseka said he was not leaving the hotel, citing the armed soldiers outside. Several dozen armed soldiers lined the street of the Cinnamon Lakeside Hotel and surrounding area, checking cars driving up to the building in the nation's capital, Colombo.

"He's ignoring the constitution to remain in power," Fonseka said of ally-turned-rival Rajapaksa.

There was no immediate reaction from Rajapaksa's government in response to Fonseka's claims.

The presidential election is the first since government forces put down a 26-year insurgency by Tamil Tiger rebels.

Video: Sri Lanka's historic election

And controversy mounted as vote tallying began.

Earlier Tuesday, top politicians vowed to block Fonseka from taking office if he won because he is not eligible to vote.

The government will fight the commissioner of elections in the Supreme Court on the issue of Fonseka's eligibility, Foreign Minister Rohitha Bogollagama vowed. Fonseka admits he is not registered to vote; 14 million Sri Lankans are eligible.

Rajapaksa and Fonseka have waged a bitter battle against each other. Both men say they are winning the election. But early returns showed Rajapaksa was leading in the race, state-run television SLRC reported.

Fonseka broke ranks with the Rajapaksa administration after he was elevated to the largely ceremonial post of chief of defense staff in July, following his retirement as army commander.

After Fonseka announced his presidential bid, the main opposition parties -- with widely diverse political ideologies -- closed ranks behind him to make him their common candidate.

The general is riding a wave of popularity after he led a military campaign to crush Sri Lanka's Liberation Tigers of Tamil Eelam. The Tamil Tigers, as they are known, fought a brutal war for decades against the government and controlled large swathes of territory at the height of their power.

Rajapaksa also claims war-hero status with the win against the Tamil Tigers last May. He is seeking a fresh mandate for his government, advocating for more development programs and jobs. And in his revised booklet, "Mahinda Chinthanaya" ("Thoughts of Mahinda"), he campaigns to ensure a "better tomorrow."

But in the lead-up to the election, the island nation just south of India has become host to escalating violence.

Three and a half hours before Sri Lankans headed to the polls, explosions that residents said sounded like mortar fire were heard. While it was unclear what Tuesday's explosions were, there have been more than 700 reports of violence ahead of the election, and at least our deaths reported, said Paikiasothy Saravanamuttu of the Center for Policy Alternatives, a branch of the Centre for Monitoring Election Violence.

There have been allegations of interference with mail-in ballots, according to the group. Most of the complaints have been against members of Rajapaksa's government, the center said.

The spokesman for United Nations Secretary-General Ban Ki-moon said last week that the U.N. chief was "concerned about the growing violence in the lead-up to the presidential election."

"The peaceful conduct of the first post-conflict national election is of the highest importance for long-term peace and reconciliation in Sri Lanka," he added.